At present, positive pressure ventilation is usually applied with large tidal volumes and only exceptionally at respiratory rates above 20 per minute. A novel method of jet ventilation uses instead of endotracheal tube a small cannula introduced transtracheally or between the vocal cords to inject jets of oxygen in the trachea. For this method, in our previous work a fluidic logic controlled ventilator was developed which is also capable of operating at high respiratory frequencies. There is no direct proof that the currently-used rates are the optimum for positive pressure ventilation and not just an expression of technological limits of present respirators. Using the jet ventilator, it was demonstrated experimentally and clinically, that high frequency jet ventilation (HFJV) up to the rate of 200 per miinute maintains satisfactory gas exchange at low intratracheal pressure and without circulatory impairment. During weaning from controlled ventilation, HFJV could be superimposed on spontaneous breathing. In the proposed research, high frequency jet ventilation at respiratory rates between 100 and 600 per minute will be studied on dogs to evaluate gas exchange in the lungs and determine the physiologic effects of HFJV on hemodynamics. It will be determined how the efficiency of HFJV will be influenced by changing inspiration/expiration ratio and changing the catheter flow characteristics. HFJV synchronized with various phases of the heart action will also be evaluated. Finally, it will be studied whether HFJV can be applied transtracheally for long-term ventilation as an alternative to the endotracheal intubation. In clinical studies, the objective is: 1. to evaluate the use of HFJV for weaning from respiratory support as an alternative to intermittent mandatory ventilation; 2. to study the use of HFJV during laryngoscopy in anesthetized patients; and 3. to study the application of HFJV through endotracheal tube for controlled ventilation in intubated patients requiring respiratory support.